This disclosure generally relates to Continuous Feed (CF) printing systems that include a processor that receives Page Description Language (PDL) input or other input from a PDL source device or other source device and supplies raster images to a CF printer.
FIG. 1 is a side view of an exemplary CF printer. A CF printer prints on a band or roll of paper as opposed to a sheet printing system that prints on discrete sheets of media. FIG. 1 illustrates a CF printer 100 that incorporates a media input roll 102, media input adapter 104, multiple printing modules 106, 108, 110, and 112, a media output adapter 114 and a media output roll 116. The media input roll 102 comprises a wound-up paper web 118, and the media input roll 102 unwinds as the web of paper 118 is fed by the input adapter 104 to a first printing module 106. The paper web 118 continues to proceed through second 108, third 110 and fourth 112 printing modules. The web 118 continues to be processed through the output adapter 114 that feeds the paper web 118 onto the output roll 116. Any paper cutting required may be performed external to the CF printer illustrated in FIG. 1. Alternatively, the paper web 118 may be fed directly to a cutter after printing, rather than being wound on the output roll 116. Other variations of a CF printer are available, such as the CF printer embodiments described in U.S. Pat. No. 6,786,149, issued to Lomoine et al., the disclosure of which is incorporated herein by reference in its entirety.
FIG. 2 is a system level block diagram of an exemplary CF printing system 200 which may include a PDL source device 202, a Digital Front End (DFE) processor 400, an exemplary CF printer 100, as described above with respect to FIG. 1, and printed material finishing devices 204.
As shown in FIG. 2, DL source device 202 may generate page data that describes a page to be printed using PDL. For example, the page to be printed may be described using a PDL based on, for example, the Adobe Postscript standard, or another standard. The PDL description of the page may be passed by PDL source device 202, via a direct or network-based connection, to DFE processor 400.
DFE processor 400 may process the PDL page description for each page to produce a raster image of each page to be printed that may be passed to CF printer 100 for printing. Processing performed by DEE processor 400 for each page of PDL may include several steps. First, DFE processor 400 may raster image process (RIP) the PDL page description received for each page to be printed to generate a set of page objects, e.g., rectangles, letters, bitmaps, etc., and coordinates for arranging each of the respective page objects on the page to be printed. Second, DFE processor 400 may render the set of generated objects for each page to be printed using a selected halftoning process to produce a rendered halftoned raster image, as addressed in greater detail below. Third, DFE processor 400 may compress the halftoned raster image. Fourth, DFE processor 400 may transmit either a compressed, or an uncompressed, halftoned raster image to a CF printer 100 for each page to be printed.
CF printer 100 may receive a halftoned raster image, decompress the received raster image if the image was previously compressed, and then print the raster image on web of paper 118 passing through CF printer 100, as described above with respect to FIG. 1. CF printer 100 may then pass the printed output on web of paper 118 to one or more finishing devices 204.
The finishing devices 204 may receive the stream of printed output on the web of paper 118, and may cut, collate, fold and/or otherwise process the web of paper 118 to produce a printed product. Such product may include newspapers, magazines, pamphlets, and/or any other printed material. These printed products may be further processed by hand and/or by additional specialized finishing equipment to meet the needs of the final product.
An exemplary CF printing system 200, as described above, may generate printed output with a page-per-minute output rate of many hundreds of pages per minute. To support such high printed page rates, media input roll 102 and media output roll 116 may rotate in locked phase to supply web of paper 118 passing through CF printing 100 to support web feed rates of many hundreds of feet per minute. By rotating at rates sufficiently high to supply web of paper 118 to CF printing 100, both media input roll 102 and media output roll 116 develop significant rotational momentum.
DFE processor 400 supplies halftoned raster images to the CF printer 100 at an average rate that matches the page-per-minute throughput of the CF printer. A CF printer operates continuously on the principle that an image will always be available for output to the continuous web of paper 118 passing through the printer. The pages of a print job may have relative positions with respect to one another on web of paper 118, so that as the printed output is processed by the respective finishing devices, the pages of the final printed output are properly collated. For this reason, the CF printer 100 cannot accommodate a skip of one or more images in the stream of raster images received from DFE processor 400.
Therefore, should DFE processor 400 fail to deliver halftoned raster images to the CF printer 100 at a sufficiently high average rate, raster image storage buffers in CF printer 100 may become depleted of all images, resulting in an error condition referred to as “clutching” During a clutching process, the CF printer terminates the current print job and engages clutches, or brakes, to slow media input roil 102 and media output roll 116.
Given that CF printer 100 operates at such high speeds, such a termination, mid-stream of a print job, may result in damage, e.g., stretching and/or tearing of web of paper 118 and/or a failure to fuse toner on portions of web of paper 118. Recovery from such a clutching operation involves a lot of human interaction in order to clean up CF printer 100, to reinitiate CF printer 100 for a second printing process and to correlate and fuse the printed output of the separately initiated runs.
To avoid clutching, the processes executed by DFE processor 400 to generate raster images for transfer to CF printer 100, the physical interface, e.g., optical cables, point to point Ethernet, etc., between DFE processor 400 and CF printer 100, and the raster image buffer maintained by CF printer 100, may be configured to assure that DFE processor 400 can supply a stream of raster images at a rate that supports the throughput rate of the CF printer.
Due to marketplace constraints, the processing speed of DFE processor 400, the throughout capacity of the physical interface between DFE processor 400 and CF printer 100, and the storage capacity of image buffers in CF printer 100, etc., all have finite capacities. Therefore, despite efforts to design a system in which clutching is less likely to occur, operational conditions may still arise that result in clutching of CF printer 100. Often, the physical interface between DFE processor 400 and CF printer 100 is the principal bottleneck.
For example, if a print job includes a large number of pages that do not compress well, the physical interface between DFE processor 400 and CF printer 100 may be required to pass a large number of larger-than-average files. Such an occurrence may result in a reduction in the average page-per-minute transfer rate of page raster images from DFE processor 400 to page raster image storage buffers in CF printer 100. Should the average page-per-minute transfer rate of page raster images into the CF printer page raster image storage buffers fall below the page-per-minute output rate of the CF printer, a net reduction in the number of page raster image files stored in the CF printer's page raster image storage buffers will occur. Should such conditions continue for a period of time longer than that planned for when the total page storage capacity of the page raster image storage buffers in the CF printer system configuration was established, the CF printer's storage buffers may become depleted of page raster image files, thereby forcing CF printer 100 to clutch.